Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2006
Publication Date: 5/12/2006
Citation: Bae, H., Kim, M.S., Sicher Jr, R.C., Bae, H., Bailey, B.A. 2006. Necrosis- and ethylene-inducing peptide (nep1) from fusarium oxysporum induces a complex cascade of transcripts associated with signal transduction and programmed cell death. Plant Physiology. 141:1056-1067. Interpretive Summary: Plant pathogens often employ toxins that kill plant cell when causing disease. Many plant pathogens, including those attacking Theobroma cacao, produce proteins classified together as Nep1-Like-Proteins (NLP) that kill plant cells. There is accumulating evidence that these toxic proteins are important in the disease development in many different diseases in many different crops. Using Arabidopsis as a model, we have characterized the response of plant cells to Nep1, the original member of the NPL class of toxic proteins. Short-term treatment of Arabidopsis seedlings with the protein caused rapid changes in expression of plant genes thought to promote cell death and susceptibility to disease. Using this new knowledge of how plant cells respond to these toxic proteins it may be possible for scientists to develop plants resistant to the many pathogens that use the toxin when causing disease. Since this class of toxic proteins is produced by many plant pathogens, producers of many different crops could benefit from this research.
Technical Abstract: Treatment of Arabidopsis thaliana with Nep1, a necrosis and ethylene inducing protein from Fusarium oxysporum, inhibited root growth and cotyledon development. Nep1 treatment also triggered cell death generating necrotic spots and caused breakdown of the chloroplast internal membrane structures. The chlorophyll a fluorescence ratio, 685/730 nm (F685/F730), significantly decreased after 75 min treatment with Nep1 compared to the control, suggesting a short-term compensatory photosynthetic response for the localized damages to cell membranes. Based on GC-MASS analysis, the concentrations of most metabolites analyzed were reduced in Arabidopsis seedlings after 6 hours of Nep1 treatment, indicating that cell membranes had become leaky. Microarray results showed that short-term treatment with Nep1 altered expression of many genes encoding proteins putatively localized to organelles, especially chloroplast and mitochondria. Short-term treatment with Nep1 induced multiple classes of genes involved in reactive oxygen species production and signal transduction, ethylene biosynthesis, membrane modification, apoptosis, and stress. Real-time PCR was used to confirm the induction of genes localized in the chloroplast, mitochondria and membrane, and genes responsive to calcium/calmodulin complexes, ethylene, jasmonate, ethylene biosynthesis, WRKY, and cell death. Our molecular data suggested that salicylic acid is not associated with the early response to Nep1. Nep1 rapidly altered expression of many genes involved in organelle function and associated with senescence and cell death. Cell death occurred in all tissues of Arabidopsis seedlings and damage to internal chloroplast membranes was probably due to the indirect effect of Nep1, such as ethylene and/or reactive oxygen species and other processes, which lead to senescence and cell death.